When a laser nephelometer measures the concentration of plasma protein and pharmacon in a tested solution, the dust, air bubbles and other substances (e.g. lipoprotein, denatured protein) inherently present in that solution usually become the main error causing elements. Accordingly, if the effect of these elements on the scattered data should be eliminated, this would result in a more accurate and reliable measurement.
The Japanese patent public disclosure No. 90883/1976 describes an apparatus for measuring the concentration of light reflecting substances in a solution. Out of the sampled data elements, only the element representing the scattered light having the least intensity is accepted while any other data element is rejected. The apparatus uses this minimum data element as a "measured value". Further, this patent public disclosure contemplates a method of reducing the effect of dust particles and air bubbles by differentiating a momentary pulsed output resulting from the scattering caused by those particles and bubbles from the uniform output resulting from the substances which are the object of measurement.
The method as disclosed in the Japanese Patent Public Disclosure No. 120485/1978 stores all observed data elements and changes their order in accordance with the data value indicative of the scattered light intensity at the time of sampling so that the data element having the minimum value is placed in the first position. A predetermined number of data elements including and following the minimum data element are all added together and averaged. The average value is indicated by indicating means in the form of digital representation or print out.
However, dust particles and air bubbles present in suspension in the small space where the laser beam travels cannot be taken out from that space. Accordingly, the above average with respect to the predetermined number of data elements including and following the minimum data element may still have, to a certain extent, error factors due to those dust particles and air bubbles.